The lazy state-transformer monad. A computation of type ST s a transforms an internal state indexed by s, and returns a value of type a. The s parameter is either
* an unstantiated type variable (inside invocations of runST), or
* RealWorld (inside invocations of stToIO).
It serves to keep the internal states of different invocations of runST separate from each other and from invocations of stToIO.
The >>= and >> operations are not strict in the state. For example,
> runST (writeSTRef _|_ v >>= readSTRef _|_ >> return 2) = 2

The strict state-transformer monad. A computation of type ST s a transforms an internal state indexed by s, and returns a value of type a. The s parameter is either
* an uninstantiated type variable (inside invocations of runST), or
* RealWorld (inside invocations of Control.Monad.ST.stToIO).
It serves to keep the internal states of different invocations of runST separate from each other and from invocations of Control.Monad.ST.stToIO.
The >>= and >> operations are strict in the state (though not in values stored in the state). For example,
> runST (writeSTRef _|_ v >>= f) = _|_

A monad transformer embedding lazy state transformers in the IO monad. The RealWorld parameter indicates that the internal state used by the ST computation is a special one supplied by the IO monad, and thus distinct from those used by invocations of runST.

A monad transformer embedding strict state transformers in the IO monad. The RealWorld parameter indicates that the internal state used by the ST computation is a special one supplied by the IO monad, and thus distinct from those used by invocations of runST.

State monads.
This module is inspired by the paper Functional Programming with Overloading and Higher-Order Polymorphism, Mark P Jones (http://web.cecs.pdx.edu/~mpj/) Advanced School of Functional Programming, 1995.

Strict state monads.
This module is inspired by the paper Functional Programming with Overloading and Higher-Order Polymorphism, Mark P Jones (http://web.cecs.pdx.edu/~mpj/) Advanced School of Functional Programming, 1995.

Strict state monads, passing an updatable state through a computation. See below for examples.
In this version, sequencing of computations is strict. For a lazy version, see Control.Monad.Trans.State.Lazy, which has the same interface.
Some computations may not require the full power of state transformers:
* For a read-only state, see Control.Monad.Trans.Reader.
* To accumulate a value without using it on the way, see Control.Monad.Trans.Writer.

The strict WriterT monad transformer, which adds collection of outputs (such as a count or string output) to a given monad.
This version builds its output strictly; for a lazy version, see Control.Monad.Trans.Writer.Lazy, which has the same interface.
This monad transformer provides only limited access to the output during the computation. For more general access, use Control.Monad.Trans.State instead.

A state monad parameterized by the type s of the state to carry.
The return function leaves the state unchanged, while >>= uses the final state of the first computation as the initial state of the second.